Accelerometers based on MEMS transducers generally sense movement using a movable central mass that is oriented between fixed beams. For example, a set of beams are coupled to the movable central mass and can be deflected from a rest position by subjecting the system to acceleration. As the beams attached to the central mass move, the distance between these beams and the fixed beam to one side increases by the same amount that the distance to the fixed beam on the other side decreases. This change in distance may be used to measure acceleration.
In many cases, MEMS accelerometers are over-molded to produce a packaged sensor, and this over-molding may impart a stress on the accelerometer. This stress may vary with temperature and time to produce a drift, which has a hysteresis characteristic in the stress behavior of the structure. For example, the profile of this stress can change depending on the environment (e.g., in response to a tester or a particular application) and the time behavior of the properties of the MEMS structure. The stress may result in an offset behavior that is difficult to predict. Offset behavior in the signal chain of the accelerometer can cause asymmetric clipping, resulting in offset shifts at the output of the sensor. In some accelerometers, force feedback is used in an attempt to remove non-linearities and errors from the output signal. While force feedback may be modeled for simple behaviors, to account for feedback loop stability in all conditions, this method becomes complex and is similarly complicated to implement.
Accordingly, a method and apparatus for sensing acceleration having improved accuracy are desired. In addition, a method and apparatus for sensing acceleration having a low implementation complexity and that removes offset shift are desired. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.